The big industry in this pretty city in southwestern Utah is building and selling homes, and business is so good that St. George is running out of land.

Set beneath the red bluffs of the Colorado River plateau and blessed with sunshine more than 300 days a year, St. George has been one of the fastest-growing communities in the United States over the past quarter-century. Like many cities in the Mountain West, St. George is an island of private property in a sea of public land. The modern city is mostly built on homesteads that farmers claimed from the government in the 19th century, and as developers have run out of farmland to turn into subdivisions, prices have soared. Relative to local incomes, housing in St. George is more expensive than in New York.

The Trump administration is proposing to address the housing crisis in Western cities by opening some of the government’s vast landholdings for development. Last month the Interior Department and the Department of Housing and Urban Development announced a joint task force to identify parcels and expedite construction.

It’s a great idea, if it’s done right. Federal lands are a national resource, and the nation needs more housing. The proposal is easily caricatured as turning national parks into trailer parks, but there’s a lot of Western land that belongs to the government simply because no one else wanted it. It’s scrubland, not El Capitan.

The proposal won’t make a dent in the crisis, however, if the land is used for more vacation McMansions or even for single-family homes on quarter-acre lots. What cities like St. George need most — and what they mostly refuse to allow — are modest homes and apartments for low-wage workers and families.

The red bluffs above St. George should be preserved forever. The acres of barren land east of the St. George airport that the government owns because no one wanted to farm it? That should be used for apartment buildings.